1. Field of the Invention
This invention is a device for preventing reverse rotation of a shaft of a turbine or pump, or the like, while allowing unencumbered rotation of the shaft in a forward direction.
2. Description of the Prior Art
Devices for preventing reverse rotation are well known and widely employed. Commonly, a rotating shaft has a circumscribing ratchet with a lever or pawl disposed to engage teeth of the ratchet preventing rotation in a disallowed direction. A variety of schemes are used to withdraw the pawl from intercourse with the ratchet during forward, allowed rotation of the shaft. A most common technique is to employ centrifugal force generated by the rotating shaft to control the pawl.
In different systems, the ratchet may be fixed, while the pawl rotates with and is integral to the shaft, or vice versa.
For examples of prior art, refer to the following U.S. patents:
______________________________________ Antireversing Pump Head Palmer U.S. Pat. No. 1,516,681 Brake . . . Like Gornley U.S. Pat. No. 1,383,201 Restraining Device Shirley U.S. Pat. No. 3,912,192 Gravity and . . . Mechanism Whitney U.S. Pat. No. 2,687,785 Blocking . . . Vehicles Lindbald U.S. Pat. No. 4,085,905 ______________________________________
Anti-reverse rotation devices typically have a wear and noise problem associated with ratchet-pawl contact during periods (perhaps prolonged) of low shaft rotation speed. In some cases, the pawl may ride on the ratchet in a low speed range, or may even bounce in and out of engagement.
Consequently, it is desired to provide an anti-reverse rotation device which achieves total ratchet-pawl disengagement at a low shaft speed. Moreover, it is desired to achieve this while utilizing a simple mechanism using a minimum of components requiring maintenance, and with no external controls.